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Text of Chap46

  • Explain the different types of colour.
  • In This Chapter, youll learn on: Different types of Colour Management System o RGB Formula o CMYK Formula o Black & White o Duotone How to convert between colour modes such as o Black & White to Duotone o RGB to Grayscale o RGB to CMYK o RGB to Indexed. Advantages of web-safe colour tools : o 216 web-safe colours o HTML colour codes o Colour Matters / web-safe palette o Colour Logic for web-safe colours Differences between process colour and spot colour in a desktop publishing documents
  • Color plays a vitally important role in the world in which we live. Color can change actions, sway thinking, and cause reactions. It can irritate or soothe your eyes, suppress your appetite or raise your blood pressure. As a powerful form of communication, color is irreplaceable. Red means "stop" and green means "go. Traffic lights send this universal message. Likewise, the colors used for a product, web site, business card, or logo cause powerful reactions. Color models describe colors numerically. There are different methods of describing colors numerically, and a color mode determines which method or set of numbers to use to display and print an image. Photoshop bases its color modes on the color models that are useful for images used in publishing. You can choose from RGB (red, green, blue); CMYK (cyan, magenta, yellow, black) and Grayscale. Photoshop also includes modes for specialized color output such as Indexed Color and Duotone.
  • Black & White (Bitmap) In bitmap images, pixels are either black or white. This allows for incredibly small file sizes, but there is a corresponding loss of image quality. Because pixels are either black or white, they can appear jagged along the edges. At low resolutions, this can lead to a "blocky" appearance. Images that just contain only black and white dots should in most cases be scanned in 600 dpi to obtain a good quality. The exception is if the files become too large to handle, 300 dpi is in most cases acceptable. When converting a grayscale image to bitmap, the computer analyzes each pixel, and "rounds" it to either black or white. In bitmapped mode, each pixel occupies 1 bit. A pixel can either be the foreground or the background color. Bitmapped mode is mainly used for scanned line art or for special fonts or symbols to be used on the web.
  • Grayscale Grayscale is similar to bitmapped mode, but it stores shades between foreground and back-ground. Photoshop supports either 8 bit (256 shades) or 16 bit (65536 shades) resolution. This is the universal mode for anything that does not need colors. Grayscale images are 256 shades of gray. Each pixel is assigned a brightness value that gives it the gray tone. Color images can be converted to grayscale, as can grayscale images be converted to RGB or Indexed Color modes, though the color palette will be made up of gray shades. When you know your final product is going to be grayscale, it is best to work with them in color first, to get more of the subtle tones that you may want, and convert it to grayscale as a last step.
  • A grayscale image at 8 bit color depth. Close-up of the grayscale image. Notice that there are black, white, and shades of grey making up the image. Grayscale image converted to bitmap image at 96 dpi. Close-up of bitmap image. Notice that there are no tones of gray, all pixels are either black or white.
  • RGB RGB stands for the colors Red, Green and Blue. RGB are the colors that computer monitors, scanners and televisions use to show colors. Most of the images people create are RGB, and when working within your own office, it is generally the better choice when creating and processing images. The computers colors (Red, Green, Blue) is the best option for the web or electronic publishing. They are also called additive colors. Advantages of working in RGB mode include the following: o You can save memory and improve performance because you are working with fewer channels. o The range of colors in RGB spaces is much larger than that of CMYK spaces, so more colors are likely to be preserved after adjustments.
  • RGB When working in RGB color, you are working with 3 color channels. Each primary color, red, green and blue, has its own channel, and the intensity of each channel, on a scale from 0 to 255, contributes to the color per pixel. Think of it as like mixing paints. The proportions of red, green and blue used on the painter's palette create a color. If a warmer shade is desired, more red is added, with less green and blue, etc. But since white is a pure color, it is created by combining each channel at full intensity (255).
  • Colors are created in the RGB mode by assigning values ranging from 0 to 255 for each of the color channels. The overlapping areas represent the colors created by full values for each channel, in this case creating cyan, magenta, yellow, and white.
  • Even though you can perform all color and tonal corrections in RGB mode and nearly all adjustments in CMYK, you should choose a mode carefully. Whenever possible, avoid multiple conversions between modes, because color values are rounded and lost with each conversion. If an RGB image is to be used on-screen, you needn't convert it to CMYK mode. Conversely, if a CMYK scan is to be separated and printed, you needn't perform corrections in RGB mode. If you must convert your image from one mode to another, it makes sense to perform most of your tonal and color corrections in RGB mode and use CMYK mode for fine-tuning.
  • CMYK CMYK stands for the colors cyan, magenta, yellow and black. (in order to avoid confusing black with blue, its abbreviation is K instead of B) . CMYK are the colors used for full-color printing and is used more for commercial printing. If you look at a magazine close up you will see tiny patterns of dots, these dots are arranged in different patterns and sizes to fool the eye into seeing colors that are not really there, e.g. brown etc. The disadvantages are, the image is a 3 times larger than RGB, and you will lose some brightness as CMYK does not support as wide a tonal range as RGB. In this model four colors of pigment, Cyan, Magenta, Yellow and Black are printed in patterns of dots which our eyes mix to create the illusion of many different colors.
  • CMYK Unlike the RGB model, CMYK is subtractive. While in theory cyan, magenta and yellow could reproduce any color; black is added to compensate for some impurities of the inks. CMYK is the preferred color mode to use for color printing if - and only if - your printer supports it. Other than that, it has no real advantages. While cyan, magenta and yellow occur naturally, black has been defined as the absence of color, but in the publishing industry, in order to get true blacks, black had to be added to the process.
  • CMYK Like the channels of RGB color, each color of CMYK is a channel, and a pixel is assigned a percentage value of cyan, magenta, yellow and black. A smaller percentage of a color equates to a smaller amount of color available to the pixel. For instance, if a white area is desired, all values would have a 0%. Red may have a low percentage of cyan, high percentages of magenta and yellow, and no black. To create darker colors, the mixing together of inks (higher percentages of color) "absorbs" more light, therefore reflecting less and creating the darker shades.
  • Colors in the CMYK mode are created by assigning a percentage to each color channel. The overlapping areas represent the colors created by 100% of each color channel, in this case creating red, green and blue. Notice however that these shades of RGB differ from those in the image of RGB color. This is due to the difference in the way CMYK interprets and creates color.
  • Printers use the CMYK color system. But because of the difference in the way monitors see color and printers do, you can get surprises when you go to print. This difference is in part due to the nature of the mediums, and in part due to your graphics adapter. Using higher quality adapters will lead to less surprise. The important thing to remember about these color modes is that what you see is NOT what you get. There are some colors that can be displayed on screen that cannot be reproduced in CMYK printing.
  • Duotone Duotone mode is very similar to grayscale. Duotones are used when you want to add some depth or color to a black and white image, or just get a trendy effect. A duotone lets you choose 2 ink colors on your image and will print as a 2 color job on the press. Usually, it will be made up of black and one other color, though it doesn't have to be. There is also a Tri-tone -which has 3 colors and a quad-tone that has 4. You can produce some very sharp black and white (Grayscale) images with this and it is used in photography books all the time. Because duotones use different color inks to reproduce different gray levels, they are treated i